In order to improve on manual methods of cleaning printing plates, which involved bringing the rotating plate cylinders to a halt and wiping the printing plates by hand, automatic printing plate cleaners have been developed. Many automatic printing plate cleaners utilize a liquid solution to remove dust, fibers, particles, ink, or other foreign materials from a printing plate. For example, U.S. Pat. No. 5,918,545 to Pym discloses an apparatus for cleaning a flexographic printing plate by utilizing a brush roller to scrub the plate by rotating and oscillating against the plate. To increase the brush's effectiveness, a flicker bar is then utilized to intermittently engage the bristles of the brush in order to remove debris. One disadvantage of this design is that a rotating and oscillating brush can be effective to loosen foreign particles from the plate but is less effective at permanently removing the particles when compared to absorbent material such as a sponge or a cloth. Because utilizing a brush only disrupts ink residue remaining on the plate surface after the transfer of ink to the media, a significant portion of the ink is not captured and removed from the plate surface resulting in poor print quality. Another disadvantage of a brush is that it is more likely to abrade the surface of the flexographic printing plate which is made of polymeric material that is easily damaged and/or scratched. Pym also teaches a cleaning fluid applicator for supplying detergent and water to the brush roller and subsequently to the printing plate. Disadvantageously, cleaning fluid tends to remain on the plate and negatively affect print quality and also requires additional apparatus complexity and expense to allow for both the application and removal of the fluid. Accordingly, the Pym apparatus includes a drain tray configured to receive waste fluid and debris and remove both from the apparatus. Subsequently, a drying unit is positioned to provide a pressurized air stream across the length of the printing plate in order to remove excess fluid and dry the plate. Another disadvantage of the apparatus is that because the process, including the drying cycle, requires that the press be stopped, throughput of printed material is significantly reduced.
In order to provide a cleaning apparatus that does not require the use of a liquid and associated disadvantages, U.S. Pat. No. 5,322,015 to Gasparrini discloses a rotating brush cleaning system for removing debris, dust, lint, and ink from a printing cylinder. Although the process taught by Gasparrini is completely dry, disadvantageously, both a rotating spiral brush and a vacuum system are utilized. The spiral brush has the disadvantages of using a brush noted above and the vacuum system adds unnecessary cost and complexity to the cleaning system. Although Gasparrini generally teaches that the brush cleaner is periodically urged against the printing device, the brush cleaner and vacuum system can remain engaged while the press is operational thereby reducing press downtime.
Although U.S. Pat. No. 5,644,986 to Gydesen discloses a method and apparatus for cleaning flexographic printing cylinders that does not require brushes and can also be engaged while the press is operational, the method involves detaching dust, fibers, and other foreign objects by complex means of directing pressurized fluid of air, liquid, or solid matter particles on to the plate surface to loosen ink and foreign particles. The application of liquid has the disadvantages discussed above and applying solid matter particles increases the likelihood of damaging the printing plate. Although pressurized air is less likely to be abrasive, absent physical engagement with the plate surface, dry ink and other foreign particles are more likely to remain, thereby reducing print quality. Adding to the complexity of the design, a vacuum/suction and collection system is used to remove particles loosened from the plate surface by the pressurized air, liquid, or solid matter particles. This removal system has several disadvantages including the significant purchasing, operating, and maintenance costs required for the vacuum, blower and pump infrastructure. Furthermore, the effectiveness of the system is significantly reduced due to its reliance on uniform plate thickness. Because plates vary in thickness from one another and potentially across each specific surface, the precise setting of the apparatus at a specific distance from one plate surface will likely lead to diminished quality prints in successive printing plate changes.
To overcome many of the above disadvantages, a flexographic printing plate cleaner was disclosed by U.S. Pat. No. 7,011,025 to Egan, incorporated herein by reference, which utilizes a sponge pad and cloth instead of a brush thereby effectively cleaning the printing plate through absorption means while significantly reducing the likelihood of harming the surface of the printing plate. Since the sponge pad in combination with the cloth allows for increased and relatively effective absorption, the need for a vacuum system is also eliminated. The cleaning apparatus also engages the printing plate while the press is in operation to significantly reduce press downtime. However, fluid is applied to the sponge pad as it is urged against the cloth and, subsequently, against the printing plate. Although the absorbent sponge pad and cloth significantly reduce fluid residue capable of effecting print quality, the application of any amount of liquid can increase the likelihood of fluid residue which is disadvantageous. Another disadvantage is the complexity and cost associated with the means necessary to provide fluid to the apparatus and inject the fluid to the sponge pad.
Accordingly, there is a need in the art for a simple and dry cleaner apparatus for effectively cleaning at least one flexographic printing plate that does not require abrasive brushing, the deposition of cleaning fluid, or a vacuum system, while still eliminating press downtime by engaging the printing plate while the press is in operation without diminishing print quality.